Reliable ordering of fetch event handlers

[wibblymat]

As currently implemented in Chrome, it seems that fetch handlers are called in the order that they are declared, until one calls event.respondWith. However, this isn't speced as best as I can tell.

It would be nice to add wording that says that this behavior is required so that you can, for e.g., have different parts of your application create their own fetch handlers and then add a fallback handler at the end.

self.addEventListener('fetch', function(event) {
  if (/\/myapp\/subAppA/.test(event.request.url)) {
    event.respondWith(...);
  }
});

self.addEventListener('fetch', function(event) {
  if (/\/myapp\/subAppB/.test(event.request.url)) {
    event.respondWith(...);
  }
});

self.addEventListener('fetch', function(event) {
  event.respondWith(new Response('Not found', {status: 404}));
});

As I understand it, without such spec wording a UA is free to call handlers in any order.

[annevk]

This simply builds on the event model which is defined: https://dom.spec.whatwg.org/